Pipetting apparatus and method

ABSTRACT

An automatic pipetting apparatus comprises a hand-holdable pipet-operating apparatus which includes means for releasably coupling a plurality of interchangeable pipets to a low-deadspace valving structure. The valving structure operates the pipets by selectively sealing or applying suction or pressure to a pipet. A pipet driving subassembly including pressure and suction pumps is coupled to the pipetting apparatus by flexible tubes, permitting continuous application of suction and pressure to the pipet-operating apparatus as well as free movement of the pipet-operating apparatus with respect to the pipet driving subassembly.

Waited States Patent Thiers [54] PHPE'ITWG APPARATUS AND NEW-H01) inventor: Ralph E. Thiers, Woodland Hills,

Calif.

[73] Assignee: Bio-Science Laboratories,Van Nuys,

Calif.

22 Filed: July 23, 1970 21 Appl. No.: 57,720

Related US. Application Data [63] Continuation-impart of Ser. No. 860,775, Sept.

24, 1969, Pat. No. 3,607,082, Continuation-inpart of Ser. No. 541,306, April 8, 1966, Pat.

[52] US. Cl ..73/425.6, 141/26 [51] Int. Cl. .3011 3/02 [58] Held of Search ..73/425.4 P, 425.6; 23/292 R, 23/259 R; 141/18, 25, 26, 27, 28

[56] References Cited UNITED STATES PATENTS 3,310,002 3/1967 Wilburn ..73/425.6

[4 Mar. 6, 1973 10/1967 Berman et a1. ..141/25 7/1964 Oates ..73/425.4 1?

Primary Examiner-S. Clement Swisher AttorneyGriswold and Burdick, C. Kenneth Bjork and Maynard R. Johnson [5 7] ABSTRACT An automatic pipetting apparatus comprises a handholdable pipet-operating apparatus which includes means for releasably coupling a plurality of interchangeable pipets to a low-dead-space valving structure. The valving structure operates the pipets by selectively sealing or applying suction or pressure to a pipet. A pipet driving subassembly including pressure and suction pumps is coupled to the pipetting apparatus by flexible tubes, permitting continuous application of suction and pressure to the pipet-operating apparatus as well as free movement of the pipet operating apparatus with respect to the pipet driving subassembly.

29 Claims, 23 Drawing Figures PATENTEMR 6l973 $719,087

sum 10. 7

P p l E Pressure pump H M0 /or INVENTOR.

II'I'TORNE V PATENTEDHAR ems 3,719,087

SHEET 30F 7 INVENTOR. R0406 E. This 6 97' 7' ORNE Y mcmsnm' 6W 3,719,087

SHEET F 7 llI/I I IJI"'I I I \ll I I [III/I I I III INV ENTOR. R0 40/; E. Time/15 BY j 255 35 200 ATTORNEY Pmmmm 61m 3,719,087

SHEET 50F 7 INVENTOR. R0406 E. T h [6/15 K? T TORNE Y PATENTEUMR' 61915 3; 719,087

INVENTOR.

2040/2 5 Th lens QTTORNEY PIPET'IING APPARATUS AND METHOD CROSS REFERENCES TO RELATED APPLICATIONS This isa continuation-in-part of my application Ser. No. 860,775, filed Sept. 24, 1969, now US. Pat. No. 3,607,082 which in turn is a continuation-in-part of my application Ser. No. 541,306, filed Apr. 8, 1966, now U.S. Pat. No. 3,475,128.

BACKGROUND OF THE INVENTION The present invention is concerned with apparatus of the type generally referred to as automatic pipets, including those devices which may also be described as semi-automatic. A wide variety of such apparatus is known, and automatic pipets have been classified into various groups of the same or similar types. Types of automatic pipets include both dispensers and dilutors; both mobile and immobile devices; both hand operated and mechanically operated devices; syringe-operated apparatus, such as the immobile dilutor of Rosen U. S. Pat. No. 3,197,285, and stopcock-type apparatus, such as the immobile device of Jungner, U. S. Pat. No. 3,476,518, and devices employing both a syringe and a stopcock, as illustrated by U. S. Pats. Nos. 3,138,290, 3,138,294, and 3,012,863; as well as various other devices such as tilt dispensers, double-action pipettes and rubber-bulb--operated pipets. See Broughton, A Guide to Automatic Pipettes, Technical Bulletin No. 6, Association of Clinical Biochemists, Scientific Committee, (1965 Many of the devices are highly specialized, some individual devices can pipet only an invariant predetermined volume of liquid, while others require precise recalibration of syringes or the like in order to change the volume of liquid or liquids to be pipetted. Many of the devices are somewhat inflexible in that a single device cannot be employed for pipetting successive volumes of different liquids without extensive washing or cleaning of all the working surfaces each time a different liquid is to be pipetted.

Many of the automatic pipets in use are suitable for pipetting of aqueous fluids and liquids having a similar vapor pressure, but cannot be employed with low boiling liquids, such as diethyl ether, which have high vapor pressures under the conditions in which the pipet is used. The mobile devices can, in general, be moved from tube to tube as desired; however, many of the mobile devices depend on manual operation to a high degree. In contrast, the immobile devices cannot be moved during use, however, many of the immobile devices are highly automatic, providing push button simplicity of operation.

It would be desirable to provide a pipetting apparatus which is simple and accurate in operation, which is flexible in use both as to the types and volumetric amounts of liquids pipetted, and which can be mobile or immobile as desired while providing highly automatic, simple and foolproof operation.

BRIEF SUMMARY OF THE INVENTION The pipetting apparatus of the invention comprises a pipet-operating subassembly operably engageable with pipet-driving means for providing pipet-charging suction and pipet-discharging pressure thereto and selectively operably engageable with a pipet, the pipetoperating subassembly including means for selectively operably engaging the pipet-driving means with a pipet selectively to charge the pipet by suction, to seal a predetermined volume of fluid within the pipet and to discharge the pipet under pressure. The pipet-operating subassembly can be mobile with respect to the pipet-driving means, which can be adapted to provide continuous suction and pressure to the pipet-operating subassembly by means of flexible tubes or other universally movable coupling means. The pipet-operating subassembly includes low dead space valve means for controlling the charging, sealing, and discharging of pipets. Also included on the pipet-operating subassembly are means for selectively operably engaging the pipet-operating subassembly with individual pipets to permit pipetting to be carried out with any desired individual pipet of a plurality of pipets of different volumes. The pipetting apparatus can also include a novel pipet or plurality of interchangeable pipets adapted to co-act with the pipet-operating subassembly. The apparatus of the invention is simple in construction and operation, highly flexible in use, and provides mobility in use coupled with highly automatic, precise pipetting of a wide variety of fluids. The invention also provides for rapid operation while minimizing errors. Other advantages of the invention will be apparent from consideration of the following description and claims and of the drawings.

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS FIG. 1 is an isometric view of a pipetting apparatus of the invention illustrating the use thereof in pipetting;

FIGS. 2 and 3 are schematic views of the apparatus of the invention in two embodiments thereof;

FIG. 4 is a side elevational view of a representative embodiment of a pipettor of the invention partially broken away to illustrate structure of the valving means, sealing means, valve operating means and pipet receiving and retaining means;

FIG. 5 is a plan view of the pipettor of FIG. 4, partially broken away to illustrate the valve and valve operating means;

FIG. 6 is an elevational view of a second embodiment of a pipettor of the invention, partially broken away to illustrate the valve operating means, valve means, sealing means, and pipet receiving and retaining means;

FIG. 7 is a plan view of the valving means of a pipettor of the invention in one embodiment thereof;

FIGS. 8 and 9 are plan and elevational views partly in section of a valve means in another embodiment thereof;

FIGS. 10, 11 and 12 illustrate the operation valving means embodiment of FIG. 7;

FIGS. 13, 14 and 15 illustrate the operation of the valving means embodiment of FIGS. 4 and 5;

FIGS. 16, 17 and 18 illustrate the operation of the valving means embodiment of FIGS. 8 and 9;

FIGS. 19, 20 and 21 and 22 illustrate the structure and operation of the pipet, pipet receiving means, sealing means and pipet retaining means of the invention in a representative embodiment thereof;

FIG. 23 is an elevational view of a pipet and pipettor of the invention partially broken away to illustrate a of the further embodiment of the pipet and valve control means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring more particularly to FIGS. 1-3 the pipetting apparatus 30 comprises a pipet-operating subassembly, e.g., pipettor 32. Pipettor 32 includes a pipet-receiving portion 34 adapted to receive an end 35 of a pipet 36, and a manually-graspable portion, e.g., handgrip 37 adapted to fit comfortably in the hand 25 of an operator. Means for operating the pipet 36, such as hollow suction and pressure lines 50, 60 for supplying suction and pressure for charging and discharging pipet 36, and the attendant valving means, e.g., valve 100, for controlling application of suction or pressure to operate the pipet 36; means for selectively sealing the end 35 of a pipet 36 in operative engagement with valve 100, e.g., gasket 200; pipet receiving means, e.g., socket 202 for guiding pipet 36 into operative engagement with gasket 200 and valving means 100; and a pipet-retainer 300 are all housed in pipettor 32, as are means for selectively operating the valve 100, e.g., button 38, and for selectively operating the pipet retainer, e.g., trigger grip 40. The pipetting apparatus 30 further comprises a pipet-driving subassembly 80. The pipetoperating subassembly 80 includes means for supplying pipet-operating suction and pressure to the pipettor 32, e.g., suction and pressure pumps 82, 84 in FIG. 2, or the intake and exhaust ports 86, 87 of a single pump 88 in FIG. 3 and the attendant hollow suction and pressure connecting lines 81, 83, liquid trap 85, trap connecting line 79, motor or motors 89 and the like. The pipetoperating subassembly 80 is preferably mounted within a unitary housing 28. Housing 28 preferably includes a receptacle 39 adapted to house the pipettor 32 when not in use, and a removable face plate 40 to provide access to the trap 85, motor and pump means and the like enclosed within housing 38. Control of the operation of the pump and motor means is conveniently provided by appropriate circuitry (conventional and not shown) operated by a switch button 41, also mounted on the housing 28. The pipettor 32 and pipet-driving subassembly 80 are operably engaged with each other by means of flexible suction and pressure tubes 55, 65 which communicate between the corresponding lines 50, 60 in the pipettor 32 and the corresponding pump means (pumps 82, 84 in FIG. 2 or intake and exhaust ports 86, 87 of pump 88 in FIG. 3) by way of connecting lines 81, 83 in the housing 28. Tubes 55, 65 are flexible to permit the pipettor 32 to be moved freely with respect to the housing 28, as may be convenient in typical operation, for example, in pipetting a given quantity of a liquid 44 from a first beaker 45 to a second beaker 46.

In operation, fluid suction (partial vacuum or reduced pressure) and fluid pressure for charging and discharging the pipet 36 are provided in the suction and pressure lines 50, 60 in pipettor 32 by means of the flexible tubes 55, 65 and pressures and suction means of subassembly 80. Suction and pressure are thus supplied in a substantially continuous fashion at the valve 100 in pipettor 32, fluctuations in fluid pressure within the system resulting primarily from the'work done in charging and discharging a pipet 36 or from pressure regulating means as described below. The pipettor 32 is universally mobile in three dimensions with respect to subassembly 80. Charging and discharging of the pipet 36 are carried out by means of valve 100 housed in the pipettor 32 whereby the pipettor-engaging end 35 of pipet 36 is selectively placed in communication with either the suction line 50 for charging or the pressure line 60 for discharging. The valving means employed also permits pipet end 35 to be sealed from communication with suction and pressures lines 50, 60 and sealed from the atmosphere as may be desired, for example, in transporting a charged pipet 36 from one beaker 45 to another beaker 46. The apparatus 30 can be further characterized in that the pipetting operation involves complete charging of a pipet 36 with a liquid 44 to be measured, an initial portion of the liquid charged into pipet 36 being employed as a pre-wash liquid in each charging operation. The valve 100 employed in the pipettor 32 mechanically divides the metered portion of a charged liquid 44 from a pre-wash portion 47, preferably by division at a single location. The pre-wash portion 47 remains in the pipettor 32, and is carried along suction line 50 and tube 55 to trap for ultimate disposal. The portion of fluid 44 metered in pipet 36 is mechanically and precisely separated from the pre-wash portion by the valve and is ultimately discharged through pipet tip 236. Complete charging of pipets 36 and mechanical division of the fluid 44 eliminates many of the problems encountered in pipetting of volatile liquids.

The volume of fluid pipetted is the total of internal volume of the pipet 36 plus the volume of a micropipet 210 which communicates with pipet 36 independently of whether valve 100 is in the sealing, charging or discharging mode of its operation. Micropipet 210, as illustrated in FIGS. l1, l4 and 17, for example, is defined by those portions of valve 100 and gasket 200 which enclose a portion of fluid 44 which is to be discharged through pipet 36. The metering operation thus does not depend upon charging to a meniscus line as in manual pipetting, or upon calibration of the displacement of a piston, as in syringe metering. The volume of the micropipet 210 of a pipettor 32 is small in relation to he volume of the pipet 36 itself. For example, the micropipet volume can be on the order of from about 1 microliter or less to about 10' to 15 microliters, or on the order of one percent or less to 10 to 15 percent or more of the total volume pipetted, depending on the volume of the particular pipet 36 employed. The volume of fluid 44 metered by the micropipet 210 is substantially uniform from one pipetting operation to another, regardless of whether the same or different pipets 36 having the same or different volumes are employed. Consequently, pipetting of different volumes is readily carried out by employing a plurality of pipets 36, each calibrated to contain and deliver a desired volume of fluid in conjunction with the micropipet 210. As will be more fully described hereinbelow, the coaction of the various pipet-operating and pipet engaging and retaining means elements of the pipettor 32 with pipets 36 of various sizes and with the other elements of the apparatus 30 provides a versatile integrated pipetting apparatus capable of rapid and accurate pipetting of fluids over a wide range of volumes.

Further advantages of the invention and additional details of the construction and operation thereof will be apparent from consideration of the following detailed description of preferred embodiments of the invention. In the following description it will be convenient to refer separately to various elements of the pipetting apparatus 30 and embodiments of such elements. For ease of reference, the same reference characters are employed from time to time in the drawings to refer to identical elements as they appear in different embodiments of the invention.

1. THE PIPET-DRIVING SUBASSEMBLY 8i CONNECTING TUBES 55, 65 AND SUCTION AND PRESSURE LINES 50, 60

The supply of pipet-driving suction and pressure at valve 100 in pipettor 32 is substantially continuous regardless of whether valve 100 is in a charging, sealing or discharging mode of operation. Consequently, it will be convenient to describe the means of supplying and regulating suction and pressure separately from a detailed description of preferred embodiments of valve 100.

Referring more particularly to FIGS. 1-3, pipetcharging suction and discharging pressure are furnished by suction and pressure pumps 82, 84 or by a single pump 88. Conventional air pumps capable of providing, for example, a partial vacuum and positive air pressure on the order of about I to 5 pounds per square inch gauge can be employed, the pumps 82, 84, 88 being driven by an electric motor or motors 89 or other suitable means. When desired, a pressurized gas cylinder, aspirator or other means for providing fluid pressure and suction can be employed, and discharge pressure can also be provided in the form of a liquid inert to the material to be pipetted, although gas pressure is generally suitable and convenient. Trap 85 can be a conventional liquid trap for preventing liquid from reaching pump 82 or 88, while maintaining a partial vacuum in line 50 and tube 55. The tubes 79, 81, 83, 55, 65 and suction and pressure lines 50, 60 are conveniently flexible, hollow tubing of a polymeric material such as polyethylene, rubber, plasticized polyvinyl chloride, polypropylene, or the like, and are preferably resilient and transparent. Flexible tubing having an inside diameter of from about 1 to about 10 millimeters and an outside diameter of from about 4 to about 20 millimeters, can be conveniently employed. It is preferred, however, that suction connecting tube 55 be of a material which is easily wetted by the liquid or liquids to be pipetted, a connecting tube 55 of rubber being preferred, for example, for pipetting aqueous liquids. In typical repetitive pipetting operation, suction connecting line 55 can contain several successive portions of pre-wash liquid 47 as the liquid portions are drawn under suction to trap 85. The use of a connecting tube 55 of wettable material substantially reduces the suction required to draw several portions of prewash liquid 47 from pipettor 32 to the trap 85 as well as contributing to uniformity of suction applied at valve 100 during a series of rapid successive pipetting operations. Connecting tubes 55, 65 are coupled to the corresponding connecting lines 79, 83 at the pipet-driving subassembly housing 28 and to lines 50, 60 or portions thereof in the pipettor 32 by friction fit over tubular couplings 90 or by any other suitable coupling means.

The fluid circuit connecting the valve 100 and pumps 82 and 84 or 88 can include means for regulating the pressure and suction applied at the valve 100. For example, low pressure differentials at the valving structure W0 can be desirable to provide low flow rates when small volumes (e.g., I00 microliters to a few milliliters) are being pipetted, and high pressure differentials may be desirable for more rapid charging and discharging of large volumes (e.g., 25 or 50 milliliters). Pressure and suction can be regulated independently by an adjustable screw clamp 91 on each of connecting lines 55, 65 as shown in FIG. 2. Clamps 91 may be mounted in the pipettor 32, within the housing 28, or on external portions of tubes 55 and 65 themselves. Alternately, pressure and suction pressure differentials can be regulated by a surge chamber 92 in the pressure connecting line 83, chamber 92 being vented to the atmosphere via an adjustable pressure relief valve 93. As illustrated in FIG. 3, adjustment of the pressure relief valve 93 provides direct control of the maximum pressure in lines 83 and 60, tube 65 and surge chamber 92. Valve 93 indirectly controls the suction by controlling the exhaust pressure of pump 88. Direct control of suction line pressure can be obtained by employing a similar surge chamber and pressure relief valve in the suction connecting line 81 downstream of trap 85. In convenient form the vented surge chamber 92 can comprise a short length of flexible tubing intersecting line 83 or line 81 at a T or Y intersection, with a screw clamp or other adjustable clamp for sealing the tubing against selected pressure differentials serving as valve 93. In charging a pipet 36, a pre-wash portion of liquid 47 is carried through valve 100 into suction line 50. Line 50 and the pipettor 32 preferably include a transparent portion, view port or the like to permit visual observation of line 50, so that the movement of a liquid column into line 50 provides a visible indication to an operator that charging is complete. A fixed fluid resistance 95, such as a constriction in the suction line provided by a tubular coupling in FIG. 2, is provided to impede the flow of the liquid column along the suction line 50 toward trap 85 and to reduce the volumetric liquid flow rate in line 50, after the charged liquid reaches the constriction or resistance 95. The reduction in flow rate facilitates observation of completion of charging and reduces the volume of liquid which may be inadvertently drawn into suction line 50 when sealing of the charged micropipet 210 is delayed by operator inattentiveness or the like. A similar fluid resistance or constriction 95 can be disposed in pressure line 60 to limit the volume of pressurized discharge gas which enters the valving structure at the initiation of discharging, thus providing for a steady, even flow of pressurized gas regardless of the initial pressure differential between pressure line 60 and micropipet 210 when discharging is begun. The fluid resistance or constriction 95 is preferably disposed in pressure line 60 so that the internal volume of line 60 downstream of the resistance 95 with respect to fluid flow therethrough is less than the smallest volume of fluid to be pipetted with the pipettor 32. The discharge gas volume contained in line 60 downstream of resistance 95 is preferably sufficiently small in relation to the pipet volume to provide a substantially uniform flow rate from the pipet 36 during a major proportion of the discharging operation regardless of pressure increases in the suction line 60 when the valve structure 100 is sealed.

2. THE VALVE 100 a. A First Preferred Embodiment In one embodiment thereof, the valve 100 employs principles of structure and operation described in my application Ser. No. 541,306, filed Apr. 8, 1966, now U. S. Pat. 3,475,128.

As illustrated in FIGS. 7 and 10l2, the valve 100 can comprise a relatively rigid base 102 which can be part of the pipet-receiving portion 34 of a pipettor 32, the base 102 having a partially circular movable, tubular conduit wall 104 secured thereto, portions of conduit wall 104 defining portions of suction and pressure lines 50, 60. Valve 100 also comprises a spider 106 pivotally mounted on base 102 by means of a shaft 105. Spider 106 carries rollers 109, 110, 111 rotatably mounted on the arms 108 of the spider 106, the rollers 109, 110, 111 being disposed against portions of the conduit wall 104 so as to compress opposed portions of conduit wall 104 together between each roller 109, 110, 111 and the base 102 thus forming a series of movable seals 119, 120, 121 in lines 50, 60. Conduit wall 104 is preferably of a resilient material adapted to maintain lines 50, 60 normally open. Base 102 also includes a pipet-receiving socket 202 having a gasket 200 mounted therein and adapted to sealingly engage a pipet 36. Fluid communication between lines 50, 60 and the pipet 36 is provided by a micropipet bore 210 extending through conduit wall 104, through base 102 and gasket 200. The bore 210 thus constitutes a micropipet chamber which is continuously in communication with socket 202 or the interior of a pipet 36 and which is selectively in communication with portions of lines 50, 60 within conduit wall 104 at a generally T-shaped intersection. Pressure line 60 and suction line 50 similarly communicate with other portions of lines 50, 60 externally of valve 100 via pressure and suction line bores 61, 51 through conduit wall 104 on either side of, and adjacent to the intersection of lines 50 and 60'and micropipet bore 210. Beyond suction and pressure line bores 51, 61 and more or less diametrically opposed to micropipet bore 210 on base 102, the conduit wall 104 terminates in vents 112, adapted to provide communication between lines 50 and 60 and theatmosphere. The volume enclosed by conduit wall 104 between vent 112 and micropipet 210 and including suction line bore 51 thus corresponds to that portion of a suction line 50 included in valve 100. A corresponding volume enclosed by conduit wall 104 and pressure line bore 61 constitutes a corresponding portion of a pressure line 60. The valve 100 is housed in a pipettor (not shown in FIG. 7) and coupled via continuations of lines 50, 60 and appropriate tubes to a driving subassembly.

Spider 106 is pivotally connected by a pin 116 to a push rod 170, the rod 170 being in turn connected to an actuator button 38 or control lever (not shown in FIG. 7). Linear motion of actuator button 38 and rod 115 rotates spider 106 with respect to base 102 and conduit 104, moving the rollers 109, 110, 111 and seals 119, 120, 121 along conduit wall 104 thereby sealing selected portions of lines 50, 60 and placing valve 100 in one or another of the pipet-charging, metering, and

discharging modes, illustrated in FIGS. 10-12. A torsion spring 115 secured to spider 106 and through slot 117 in spider 106, also secured to base 102, provides means for biasing the valve toward the pipet-sealing mode schematically illustrated in FIG. 11.

In the charging mode the rollers 109, 110, 111 and seals 119, 120, 121 are disposed as shown in the solid lines of FIG. 7 and schematically illustrated in FIG. 10,'

with rollers 109, 110 moving opposed portions of conduit wall 104 together to form seals 119, in the pressure line 60 between the micropipet 210 and pressure line bore 61 while leaving pressure line 60 open between pressure line bore 61 and its vent 112. Roller 111 forms a seal 121 in suction line 50 between bore 151 and vent 112. The suction line 50 is in communication with the pipet 36 through micropipet 210 and sealed from the vent 112, permitting a fluid 44 to be drawn into pipet 36, micropipet 210 and through line 50 and bore 51.

Movement of the spider 106 in a clockwise direction with respect to FIG. 7 moves the rollers 109, 110 and the seals 119, 120 formed thereby to the position illustrated schematically by FIG. 11 with portions of conduit wall 104 compressed together normally across both lines 50, 60 so that seals 119, 120 are formed in .the conduit wall portions surrounding micropipet 210.

In such position seals 109, 110 seal the fluid to be metered 44 within micropipet bore 210 and pipet 36. The movement of seal 120 across bore 210 mechanically divides the fluid 44 and seals a pre-wash portion thereof 47 in the suction line 50 to be drawn off by suction. Both the suction and pressure lines 50, 60 are open to their vents 112 in this position, the conduit wall portions 104 at vents l 12 being spaced sufficiently apart so that both vents 112 remain open when roller 111 is positioned therebetween.

Further clockwise motion of the spider 106 to the position illustrated by the broken lines of FIG. 7 results in movement of roller 109 .along conduit wall 104 toward the suction line 50, moving seal 119 across micropipet 210 to the position in line 50 shown schematically in FIG. 12. Roller 110 and seal 120 are moved progressively along the suction line 50 to suction line bore 51, thus carrying any portion of pre-wash fluid 47 to suction line bore 51, and ensuring the removal thereof from the valve 100 prior to the next cycle of operation. Roller 111 and seal 121 are simultaneously moved to seal the pressure line 70 from its vent 112, so that discharge fluid pressure from bore 61, e.g. air from pressure pump 84 or the exhaust port 87 of pump 88, is directed through line 60 into micropipet 210 and pipet 36 to discharge the metered fluid 44. After discharging, the valve 100 is returned to the mode shown in solid lines in FIG. 7 and illustrated in FIG. 10 to repeat the cycle, or to the intermediate position of FIG. 11, with micropipet 210 sealed and lines 50, 60 open to vents 1 12, for changing pipets or otherwise manipulating the pipettor prior to charging. This embodiment of valve 100 provides venting of suction and pressure lines 50, 60 to atmosphere when said lines are not in communication with micropipet 210, thereby minimizing excessive loads on the pump or pumps 82, 84, 88 and wide variations in pressure or partial vacuum in lines 50, 60. Since lines 50, 60 are open either to a vent 112 or to micropipet 210 at all times, a single pump 88 can be employed.

b. A Second Preferred Embodiment As illustrated in FIGS. 4, and 13-15, in a second embodiment, a second valve embodiment 100 comprises a rigid base 124, which can be fabricated of rigid plastic, glass, metal or the like and which can be of unitary construction with the receiving portion 34 of a pipettor 32. Mounted on base 124 are pressure lines 50 and 60, said lines having a unitary movable tubular wall 126, similar to the conduit wall 104 of the embodiment described above. A micropipet 210 extends through base 124 and a tube wall 126, forming one arm of a three-way intersection with suction and pressure lines 50, 60. A double torsion spring 130 is mounted on pin 134 within pipettor 32, having a tail portion 131 thereof securely mounted within the pipettor body 132. First and second movable arms 128, 129 of spring 130 are disposed across lines 50, 60 to maintain the lines normally closed by compressing opposed portions of tube wall 126 together against base 124 as shown in FIG. 14. First and second levers 136, 137 are pivotally mounted within pipettor 32 on pin 134, a portion of each lever 136, 137 extending under one of the respective arms 128, 129 of spring 30. Charge and discharge control buttons 138, 139 are slidably mounted in the pipettor 32, extending internally thereof through the pipettor body 132 to operably engage first and second levers 136, 137, respectively. Upon manual depression of the charge control button 138 lever 136 moves pivotally on pin 134 as a fulcrum, lifting spring arm 128 from the tube wall 126 of line 50, thereby opening suction line 50 for charging as illustrated in FIG. 13. Similarly, depression of button 139 moves lever 137 pivotally on pin 134, lifting spring arm 129 from tube wall 126 and base 124 and opening pressure line 60 for discharging as illustrated in FIG. 15. In the absence of manual depression of buttons 138, 139, both spring arms 128, 129 are biased against portions of tube wall 126 to compress the same against the opposed wall portions surrounding micropipet 210 thus sealing lines 50, 60 from the micropipet bore 210 as shown in FIG. 14. The bias provided by spring 130 also serves to lift both control buttons 138, 139 through the action of the spring arms 128, 129 on levers 136, 137 returning them to a normal, undepressed position.

The valve base 124 preferably includes a rigid spring arm stop 125 extending upwardly therefrom toward spring arms 128, 129 a distance greater than the thickness of a wall of tube 126 and preferably slightly less than twice such wall thickness. When the arms 128, 129 are in line sealing engagement with tube wall 126, stop 125 limits their motion toward base 124. The thickness of stop 125 is selected so that a spring arm 128, 129 can be biased against tube wall 126 with a force far in excess of that required to seal lines 50, 60 without unduly deforming or damaging the tube wall 126. Stop 125 permits compression of tube wall 126 by the spring arms 128, 129 to a distance less than two wall diameters to enhance sealing and bring about deformation of the tube wall 126 suflicient to seal any internal surface imperfections, while preventing undesired volumetric distortion of lines 50, 60 at the intersection with the micropipet bore 210. By employing a stop 125, lines 50 and 60 can be sealed while employing line pressures much greater than would otherwise be possible without damage to the tube wall 126.

The micropipet 210 is cylindrical, and the spring arms 128, 129 are preferably disposed for movement in parallel planes tangential to diametrically opposed walls 211, 212 of the micropipet 210. Such arrangement facilitates precision sealing since the portion of the tube wall 126 moved by a spring arm 128, 129 then is compressed against an opposed wall portion which is tangential to micropipet 210, that is, at the intersection of the tube wall 126 with one of the opposed walls 21 1,

212 of the micropipet 210. Sealing of one or another of lines 50, 60 in this manner serves to convert the threeway intersection of lines 50, 60 and bore 210 to a twoway intersection of bore 210 with a single one of the lines. When the volume defined by the tube wall 126, e.g., lines 50, 60, has the same diameter as micropipet bore 210, the two-way intersection thus formed has a substantially circular cross-section of substantially the same diameter as the micropipet bore 210 and open line (50 or 60 as the case may be) and has a substantially smooth wall. Such structure within the valve reduces or eliminates eddy currents during charging and reduces the volume of pre-wash fluid necessary to prevent carry-over of liquid from one pipetting operation to the next.

As shown in FIGS. 4 and 5, lines 50, 60 extend beyond the valve structure 100 and pipettor 32, being enclosed within the pipettor handgrip 37 and ultimately coupled to the suction and pressure connecting tubes 55, 65. The pipet-receiving portion 34 of the pipettor 32 includes a gasket 200 of rubber, silicone rubber or the like seated against the base 124 of valve structure and a pipet-receiving socket 202 adapted to enclose an end 35 of a pipet 36. A pipet 36 enclosed within the socket 202 and seated against gasket 200, is selectively retained in position by a trigger-grip type of retainer 300. Retainer 300 includes a pipet-gripping contact 302 of rubber or the like adapted to functionally engage the pipet, and a trigger grip 40. The retainer 300 is mounted on pipettor 32 for pivotal movement with respect thereto, conventional mounting means, e.g. a flange 306 and pin 308, being employed. A torsion spring 310 mounted on pin 308 maintains retainer 300 normally biased toward a pipet-retaining position illustrated in FIG. 4 with contact 302 biased toward socket 202. A pipet 36 is gripped between the contact 302 and the opposed wall of the socket 202, e.g., the pipetreceiving portion 34 of pipettor 32.

With a pipet 36 thus engaged, and the suction and pressure lines 50, 60 connected to the appropriate suction and pressure pumps 82, 84 this embodiment of valve 100 is operated as illustrated in FIGS. 13-15. Manual depression of control button 138 disengages spring arm 128 from tube 126, opening line 50. As shown in FIG. 13, a column of fluid to be pipetted 44 is drawn into pipet 36, micropipet 210 and suction line 50. Release of charge control button 138 allows arm 128 to compress tube 126, sealing line 50 and dividing pre-wash fluid portion 47 in suction line 50 from the metered fluid 44 in the pipet 36 and micropipet 210 (FIG. 14). The pre-wash fluid portion 47 is continuously subjected to suction in line 50 regardless of further operation of the valve 100 and is ultimately drawn off along suction line 50 and connecting line 55. In discharging, control button 139 is depressed so that lever arm 137 pivots and disengages spring arm 129 from tube 126 to open pressure line 60. Suction line 50 remains sealed tangentially of micropipet bore 210 as shown in FIG. 15 while gas pressure provided through line 60 discharges the metered fluid 44 from the micropipet 210 and pipet 36.

c. A Third Preferred Embodiment in the embodiment illustrated in FIGS. 6, 8, 9 and 16-18, the valve 100 comprises a base 150 mounted in the pipettor body 132 by conventional mounting means, e.g., mounting screw 151. A gasket 200 is mounted against base 150 and within socket 202. A cylindrical bore, micropipet 210, extends through gasket 200 and base 150. A pair of cylindrical studs 154 extend from base 150 a short distance, for example, 0.1 to 2 millimeters, beyond the upper face 153 of base 150. A hollow stud 155 also extends beyond the upper face 153 of base 150 and surrounds micropipet 210. Hollow stud 155 terminates in a sealing face 152, the face 152 preferably being a planar sealable surface in a plane normal to the axis of micropipet 210 and extending radially outward from micropipet 210 a distance preferably between one and two times the diameter of micropipet 210.

Valve 100 also comprises a block 160 which defines the portion of suction and pressure lines 50, 60 within the valve 100, block 160 being rotatably mounted on base 150 by a pivot pin 164 which is secured to base by conventional means, e.g., locking pin 165. Means for rotating block 160 are mounted thereon, including a radial arm 168 extending outwardly from block 160 and pivot pin 164, and connecting rod 170 pivotally coupled to arm 168 by a pin 169. Rod 170 is coupled at another portion thereof to control lever 172 and control button 38, so that reciprocating linear motion of button 38 and lever 172 is translated via rod 170, pin 169 and arm 168 to produce reciprocating rotary movement of block 160 about pivot pin 164.

Block 160 includes a face 162 slidably engaged against the studs 154 and sealing face 152 of hollow stud 155 so that face 162 can be slidingly and sealingly engaged with the face 162 of hollow stud 155 at all times. Block 160 is biased toward slidingly scalable engagement with hollow stud 155 by a conventional biasing means, e.g., spring washer 166 mounted on pin 164, the biasing pressure being distributed among studs 154 and stud 155. A flexible-walled suction line portion 53 and a flexible-walled pressure line portion 63 are coupled to'block 160 by hollow tubular couplings 52, 62 to communicate with the respective corresponding lines 50 and 60 which extend through the block 160 and face 162. The pressure and suction lines 60, 50 as defined by the block 160 are of the same cross-sectional configuration and area as micropipet bore 210. It is preferred that the portions of lines 50, 60 in the region of the block face 162 be cylindrical bores in block 160 through face 162 having their axes parallel to the axis of micropipet 210 so that alignment of either of lines 50, 60 with micropipet bore 210 as illustrated in FIGS. 16 and 18 defines a continuous, smooth walled tubular bore extending through the valve 100 from the gasket 200 through base 150, stud 155 and into block 160.

The base 150 and block 160 can be fabricated from rigid materials which are inert to the fluids to be pipetted. For example, glass, high density polyethylene, acrylic resins, polytetrafluoroethylene, stainless steel and the like can be employed. The base must be of material which is sufficiently rigid to prevent significant detectable deformation or volumetric distortion in the micropipet 210 under conditions of use and must also be resistant and inert to the fluids to be pipetted. The face 162 of block 160 also contacts the pipetted fluid and serves to seal and define the volume of fluid metered in the micropipet 210, and should likewise be resistant and inert to the fluid as well as being dimensionally stable in use. Glass or stainless steel and polytetrafluoroethylene polymers are preferred materials for fabrication of block 160. Additionally, it has been found that improved precision and ease of operation can be achieved when the materials of the block 160, at least at face 162, and at least the hollow stud extension of the base 150 are of different compressive strength. The differential compressive strength should be such as to provide a tight seal by compression of the sealing face stud 155 against block face 162 under the bias of spring washer 166 despite minor surface irregularities, and to provide a wiping effect during sliding motion of the block relative to base 150. Additionally it is preferred to fabricate the base 150 from material which is not wetted by the fluid materials to be handled. For general use, a base 150 of a polytetrafluoroethylene polymer, and a block 160 of stainless steel, glass or composite polytetrafluoroethylene material provide the desired hardness differential and wettability characteristics.

FIGS. l6, l7 and 18 illustrate the charging, sealing and discharging phases of a typical pipetting operation carried out with this embodiment of the valve 100. With a pipet 36 in position against gasket 200, and with the suction and pressure lines 50, 60 coupled via the appropriate couplings and connecting lines to suction and pressure pumps 82, 84 or to the intake and exhaust ports 86, 87 of a single pump 88, suction is continually applied in suction line 50 and pressure is continually supplied in line 60.

For charging, button 38 and lever 172 are manually moved toward the valve 100 rotating block 160 about pivot pin 164 and aligning suction line 50 with micropipet 210 as illustrated in FIG. 16. Pressure line 60, being spaced in block 160 a distance greater than the wall-thickness of hollow stud 155, is vented to atmosphere. When charging is completed, that is, when a column of fluid 44 has been drawn through pipet 36 and micropipet 210 into suction line 50, the control button and lever 38, 172 are moved to rotate block 160 I to the position illustrated in FIG. 17. In such rotation, block 160 seals micropipet 210, retaining the metered volume of fluid 44. In the sliding motion of block 160 relative to base 150, stud 155 and micropipet 210, the valve 100 first divides a pre-wash fluid portion 47 from the metered fluid 44 as a portion of face 162 of block 160 surrounding suction line 50 slides across the face of stud 155 while simultaneously sealing the micropipet 210 with another portion of the block face 162. Further sliding motion of block 160 vents the suction line 50 to atmosphere as the pre-wash fluid 47 is drawn off along line 50, also providing air washing of line 50 during the sealing and discharging phases.

When discharging is desired, control button 38 and lever 172 are manually displaced away from the valve structure 100, rotating block 160 in a counterclockwise direction with respect to FIG. 8. Pressure line 60 is thereby aligned with micropipet 210 for discharging, while suction line 50 remains vented to atmosphere as illustrated in FIG. 18.

In each of the above-described three embodiments, the valve 100 provides selective communication of the micropipet 210 with one or another of the suction line 50 or pressure line 60 or selective sealing of the micropipet 210. The selective communication and sealing is carried out by moving selected wall portions of the suction or pressure lines 50, 60 to seal the lines, preferably by moving the wall portions in a plane normal to the axis of the line or lines. In the first embodiment the lines 50, 60 are sealed by compression of portions of their movable common wall, conduit wall 104 to form a series of movable seals 119, 120, 121 and moving the seals 119, 120, 121 along the suction and pressure lines 50, 60. In the second embodiment, lines 50, 60 are sealed by compressing selected movable opposed portions of the tube wall 126 together. in the third above-described embodiment, the block 160 constitutes a movable wall of both the suction and pressure lines 50, 60, the selective sealing of lines 50, 60 being carried out by moving the wall portions of said lines, i.e., block 160 with respect to wall portions of the micropipet 210, i.e., hollow stud 155 and base 150.

It will also be apparent from the above description that the valve 100 employed in-the pipetting apparatus 30 permits the surface area of the selectively established seals to be minimized. For example, in a valve 100 according to the embodiment of FIGS. 16-18 the lines 50, 60 and micropipet 210 can have a diameter of about one millimeter, with cylindrical stud 155 having an outside diameter of slightly over 3 millimeters, the resulting surface area of slidable sealing contact between stud 155 and slide plate 162 thus being less than 10 square millimeters. The minimal seal area made possible by the valving structure of the invention provides low frictional resistance in operation and facilitates rapid valve operation, as well as reducing requirements for precision fitted or milled valve surfaces.

The valve 100 provides further advantages in that operation between charging, sealing and discharging modes requires few moving parts, the required motion of the moving parts being in a single plane. In the first described embodiment the spider 106 moves in the plane of lines 50, 60 while in the second and third abovedescribed embodiments motion of the spring arms 128, 129 or block 160 is in a plane transverse, and preferably normal to the plane of lines 50, 60. The motion required can be easily limited to short distances, for example, from one, to three, to six times the diameter of micropipet 210, or lines 50, 60. In contrast to syringe metering devices, the degree of motion in the valve 100 is independent of the volume of liquid pipetted. In contrast to pipetting devices employing conventional stopcocks, the valve 100 of the invention requires relative motion of sealingly engaged surfaces at no more than a single slidable sealed planar interface, e.g., the interface of stud 155 and slide plate 162.

From the foregoing description it will be apparent that valve 100 is adapted to divide a charged liquid into two continuous portions by mechanical separation of the fluid at single location. While the valve 100 can be modified to separate fluid at a plurality of locations, mechanical separation at but a single location in the fluid stream provides significant advantages in pipetting of volatile liquids. Since the pre-wash portion 47 is continuously exposed to the action of the suction means employed, vaporization of the pre-wash portion of liquid 47 creates no back pressure against any releasable seal formed by the valve 100. Mechanical separation of the pipetted liquid 44 in valve also eliminates head space within pipet 36 and micropipet 210, reducing the hazard of premature discharge brought about by vapor pressure of the pipetted liquid. The pipetting apparatus 30 of the invention can be employed in pipetting volatile liquids such as ether which cannot be handled in many conventional automatic pipets.

3. THE PlPET-RETAINING MEANS AND PIPETS The pipet-receiving portion 34 of pipettor 32 defines the pipet-receiving socket 202 which is adapted to receive the pipettor-engaging end 35 of a pipet 36 and guide the same into sealing engagement with gasket 200. In the embodiment of FIG. 4, socket 202 has the form of a cylindrical bore in pipet-receiving portion 34, and generally conforms to the cylindrical end 35 of pipet 36. A trigger-like pipet retaining member 300 is pivotally mounted on pipettor 32 and biased toward pipet gripping engagement of a pipet 36 between a pipet-gripping portion 302 of member 300 and an opposed wall portion of cylindrical socket 202. Pipets 36 of the same or different volumes can be interchangeably engaged with the pipettor 32 by applying manual pressure on release trigger 40 to displace the pipet gripping portion 302 of member 300 from socket 202. The pipet 36 can be withdrawn from socket 202 manually or allowed to slide free of its own weight to be replaced with another pipet 36.

The pipet or pipets 36 employed with the pipettor 32 in the embodiment of FIG. 4 are generally tubes of transparent, dimensionally stable and chemically inert material such as glass, having a tapered tip 236 through which liquids are charged and discharged, and are of generally circular cross-section as in conventional pipets. However, the pipets 36 of the invention each have a pipet-engaging portion 35 of predetermined outside diameter and length adapted to fit within the socket 202 of a pipettor 32. Portion 35 of each pipet 36 terminates in a smooth, flat sealing face 235 adapted to be sealed against gasket 200 about micropipet 210. The pipets 36 of the invention are calibrated to deliver and contain a predetermined volume between the tip 236 and sealing face 235, and include indicia 238 in standard volumetric units to indicate the total volume to be delivered by the pipet 36 when employed in conjunction with the pipettor 32. indicia 238 thus can indicate a volume different from the internal volume of the pipet 36 between the tip 236 and sealing face 235 thereof, the difference between the indicated volume and the pipet volume corresponding to the volume of the micropipet 210 of the pipettor 32.

Referring more particularly to FIGS. 20-23, a preferred pipet 36 has indicia 238, tip 236, sealing face 235 and pipettor-engaging portion 35 as in the abovedescribed embodiment. The pipettor-engaging portion 35 of pipet 36 also includes a circumferential collar 240 extending outwardly from the pipet 36 a predetermined distance from the sealing face 235, and a frustoconical beveled end portion 242 surrounding sealing face 235. Collar 240 can be integrally formed of the same material as the pipet, or it can be fabricated separately and secured to the pipet 36. In a larger volume pipet 36 which includes an enlarged portion of increased cross-sectional diameter, the enlarged portion will be intermediate the collar 240 and the tip 236.

The pipet-receiving portion 34 of a pipettor 36 includes a socket 202, and gasket 200 surrounding micropipet 210. The socket 202 comprises an inner cylindrical portion 248 adapted to receive an end portion 242 and sealing face 235 of a pipet 36 and guide the pipet 36 toward sealing engagement of sealing face 235 with gasket 202 so that micropipet 210 communicates with the interior of the pipet 36. Socket 202 further includes a flared frusto-conical portion 250 which comprises an outwardly flaring extension of the inner cylindrical socket portion 248. The pipet-receiving portion 34 of pipettor 36 includes a narrow lip 252 at the periphery of the flared socket portion 250. The lip 252 is adapted to slide under the face 235 of a pipet 36 resting horizontally on a flat surface, so that lip 252 can slide along beveled end portion 242, guiding pipet portion into flared socket portion 250. The pipet 36 and pipet receiving portion 34 of pipettor 32 thus coact to enable a user to engage a pipet 36 which is resting horizontally on a counter top or in a drawer, for example, in a one-handed scooping motion, utilizing pipet-receiving portion 34 as a scoop.

Also mounted on the pipettor 36 are a pipet retaining member 300 pivotally mounted by means of pivot pin 306, and a hand graspable release trigger 40, pivotally mounted on pipettor 36 by pivot pin 307. Retaining member 300 and trigger are mechanically linked by connecting rod 308 and pivot pins 309. Retaining member 300 includes a pair of fork arms 310 adapted to receive the cylindrical pipet engaging portion 35 of a pipet, and a partially conical pocket 312 adapted to nestingly receive the collar 240 of a pipet 36 and support the pipet by collar 240. Retainingmember 300 is normally biased toward a pipet-retaining position shown in FIG. 22 by conventional biasing means, e.g. spring 314. In such position fork arms 310 extend at least partially across flared portion 250 of socket 202, with the pocket 312 centered along the axis of socket 202 and opposed to gasket 200 and micropipet 210. The retaining member 300 is spaced from gasket 200 a distance preferably slightly less than the predetermined length of the pipets 36 from collar 240 to scaling face 235, so that the sealing face 235 of the pipet 36 is urged into firm sealing contact with gasket 200 by the nesting engagement between the pipet collar 240 and retaining member pocket 312. The bias provided by spring 314, trigger 40 and rod 308 is sufficient to maintain sealing pressure of pipet sealing face 235 against gasket 200 regardless of the orientation of the device, the volume and weight of the pipet 36 or whether or not the pipet 36 is filled with liquid. The inner lip 252 of flared socket portion 250 can include a rigid retainer stop 320 adapted to limit movement of retaining position. The stop 320 limits movement of retaining member 300 and a pipet 36 engaged thereby beyond a position in which undesirable deformation of gasket 200 can occur under pressure of the sealing face 235 of a pipet 36, while permitting sufficient movement toward the gasket 200 and sufficient deformation thereof to ensure sealing of the pipet 36 and gasket 200. Since stop 320 is adapted to limit the deformation of gasket 200 beyond a predetermined maximum, the bias provided by spring 314 can, if desired, be far in excess of that required to seal a heavy pipet 36. In ordinary usage, the pipets 36 are sufficiently similar in weight and gasket 200 has sufficient dimensional stability so that the precise placement of stop 320 is not critical. Stop 320 may generally be omitted if desired.

Retaining member 300 is pivotally movable (by manual pressure on trigger 40, for example) with respect to socket 200 between the retaining position of FIG. 22 to a pick-up position of FIG. 20. In the pick-up position the fork arms 310 and pocket 312 are displaced from the flared socket portion 250 a distance sufficient to permit free placement of a pipet 36 between fork arms 210 and nesting of pipet collar 240 in pocket 312, or permitting the pipet 36 to be disengaged from the retaining member 300, for example, to be replaced by another pipet 36.

In operation, manual pressure is applied to trigger 40 to move retaining member 300 to the pick-up position of FIG. 20. A pipet 36 is then positioned between fork arms 310 with the collar 240 nested in pocket 312, for example, by manually seating the pipet 36 or by moving the pipettor 32 toward a pipet 36 standing vertically in a pipet rack (not shown) to engage the pipet 36 between fork arms 310. When trigger 40 is released, retaining member 300 rotates on pin 306 toward socket 202, inserting portion 35 of pipet 36 into socket 202. As shown in FIG. 21, the beveled end portion 242 of pipet 36 can slide along the wall of flared socket portion 250 into cylindrical socket portion 248 as the retaining member 300 moves. Pipet collar 240 is free to tilt pivotally in pocket 312 as the pipet sealing face 235 is guided toward gasket 200 by the sliding engagement of pipet portion 35 and beveled portion 242 against the walls of socket 202. When the retaining member 300 reaches the pipet-retaining position illustrated in FIG. 22, further motion is prevented by sealing engagement of pipet sealing face 235 with gasket 200 surrounding micropipet 210 or by stop 320, when employed. Cylin drical socket portion 248 need not be of the same diameter of the pipet 36, so long as it is adapted to guide the pipet sealing face 235 into sealing engagement with gasket 200 so that the micropipet 210 communicates with the interior of the pipet 36.

The pipettor 32 and pipets 36 of the invention can thus operate to pick up, engage and disengage pipets 36 without requiring manual handling of the pipets 36 themselves. The freely-movable nature of the pipettor 32 and the cooperative structural elements of the pipet engaging portion 34, retaining member 300 and the pipets 36 themselves facilitate pick up, engagement and operative sealing of pipets 36 from the two positions most frequently encountered in laboratory pipetting, that is, horizontal position of pipets 36 lying on a counter top or in a drawer, for example, or the vertical position of a pipet 36 in a rack.

4. MEANS FOR OPERATING VALVE 100 Both the first and third above-described valve embodiments are controlled by means of a push rod 170, connecting a rotatable element of the valve 100 to a control lever 172 and control button 38 movably mounted on the pipettor 32. Lever 172, as illustrated in H0. 6 is pivotally mounted with pipettor 32 on a shaft 190, mounted in the pipettor and extending through a slot 192 in lever 172. Mounting of lever 172 on shaft 191 also includes means for biasing the lever 172 outwardly from shaft 191, e.g., spring 176. The opposed end of lever 172 extends through a slot 191 in the pipettor body 132, terminating in button 38. The inner surface of pipettor body 132 along the sides of slot 191 defines a track 175. Lever 172 includes an outwardly projecting rod 174 on each side thereof, rod 174 being adapted to move slidingly along track 175, and being normally biased toward sliding contact with track 175 by the action of spring 176. Slot 191 is bounded at opposed ends thereof by a forward or charge-position stop 177 and a rearward or discharge-position stop 179, stops 177 and 179 comprising portions of pipettor body 132 at the forward and rearward boundaries of slot 191. Stops 177 and 179 correspond to the positions of rod 174 and control lever 172 when the valve 100 is in the charging or discharging modes, respectively. Intermediate stops 177 and 179, track 175 includes a notch 178 adapted to receive rod 174 when the lever and rod 172, 174 are in a position corresponding to the sealing mode of valve 100. By means of notch 178, positive locking of lever 172 in a valve-sealing position is obtained by sliding the rod 174 along track 175 until rod 174 is seated in notch 178 under the urging of spring 176. Such positive locking of control lever 172 ensures against accidental charging or discharging as well as indicating to an operator when control button 38 has been moved sufficiently to put valve 100 in the pipet-sealing mode. The control button 38 and lever 172 can be moved manually to provide partial opening of either the suction or discharge lines 50, 60 in valve 100 when immediate manual control of the charging or discharging rate is desired. Inadvertent movement of the valve 100 beyond a charging or discharging position is prevented by stops 177, 179. As illustrated in FIG. 23, the pipettor 32 includes a valve 100, micropipet 210, gasket 200, socket 202, retaining member 300, suction and pressure lines 50, 60 and valve control button 38, control lever 172 and connecting rod 170 substantially similar to those of the embodiment described above. In the embodiment of P10. 23, control lever 172 includes an outwardly projecting rod 174 which under the bias of spring 176 rides in a track 175 internally of the pipettor body 132. Rod 174 is adapted to slide along track 175 between a forward charge-position stop 177 and a rearward dischargeposition stop 179, substantially as described with respect to the embodiment of FIG. 6. Track 175 has a concave curvature extending from stops 177, 179 toward notch 178 and outwardly from shaft 191 so that rod 174 is normally biased by spring 176 for cam-like, sliding movement along track 175 to a valve-sealing position. Rod 174 can be disengaged from notch 178 by manual pressure on control button 38 permitting manual movement of button 38 and lever 172 toward a discharging position or a charging position. Upon release of control button 38, lever 172 is returned to the valve sealing position by the biasing action of spring 176 and cam-like engagement of rod 174 and track 175. Such control means provide automatic return to a valve sealing position upon release of control button 38 whether or not release is intentional.

The pipettor 32 of FIG. 23 can also include electrical valve control means and a further modification of pipet 36. As shown in FIG. 23, the pipet 36 includes a tip 236, collar 240, sealing face 235, and indicia 238 as described above with respect to other embodiments thereof. In addition, pipet 36 carries a strip 250 of electrically conductive material such as steel, brass, copper, silver or the like extending about the collar 240 and along the exterior of pipet 36 to the tip 236. The socket 312 of retaining member 300 includes a surface of similarly conducting material, e.g., contact 252 which is connected via a lead 254 housed within member 300 and the pipettor 32 to a source of electric current. The valve includes an electrically conductive contact in the suction line 50, e.g., an electrically conductive suction line coupler 256 of silver, stainless steel, brass or the like, in the suction line 50. Coupler 256 is connected via lead 258, solenoid 260 and lead 262 to a source of current. With a pipet 36 operatively engaged in the pipettor 32, lead 254, contact 252, strip 250 and coupler 256, lines 258 and 262 and solenoid 260 define an open electric circuit adapted to operate the solenoid 260 upon closing the circuit between strip 250 at the pipet tip 236 and the suction line coupler 256. When pipet tip 236 is immersed in a liquid electrolyte 44 to be pipetted, for example, from a test tube 264, and valve 100 is in the charging mode, the normally open circuit between pipet tip 236 and coupler 256 will be closed by the liquid electrolyte 44 charged into pipet 36, micropipet 210 and suction line 50 to coupler 256. The closed circuit, and resulting opera tion of the solenoid 260 thus serves as means for electrically sensing completion of charging. Audible or visible signal means such as a buzzer or indicator light can be employed in the circuit in lieu of or in addition to solenoid 260.

In addition, control lever 172 can include a second outwardly projecting rod 180 adapted to ride along an opposed track 185 defined by surface of a catch lever 182 facing track 175. Catch lever 182 is pivotally mounted to pipettor body 132 on an internal flange 183. Track 185 and catch lever 182 are normally biased toward sliding engagement with rod 180 by solenoid spring 261, when the solenoid 260 is not activated by a current. A step or catch 186 is included in track 185 to receive rod 180 when control lever 172 is in the forward or charging position. Catch 186 is adapted to retain rod 180 and thereby control lever 172 in such position against the bias of spring 176, track and rod 174 in the absence of manual pressure on button 38 or activation of the solenoid 260. In operation, control button 38 is manually pushed to the charging position and released, the control button 38 and lever 172 being maintained in the charging position by rod and catch 186. During charging liquid electrolyte 44 is drawn into pipet 36, micropipet 210 and into suction line 50 to contact the coupler 256, closing the electrical circuit through lead 254, contact 252, strip 250, coupler 256, leads 258 and 262 and the solenoid 260,

and activating the solenoid 260. When solenoid 260 is activated, lever 182 is pivotally moved clockwise with respect to FIG. 23, disengaging the catch 186 from rod 180 and permitting control lever 172 to return to the valve sealing position. The solenoid-actuated return of control lever 172 operates valve 100 via connecting rod 170, thus dividing the liquid 44 in pipet 36 and micropipet 210 from the pre-wash portion of liquid in the suction line 50 and opening the solenoid circuit, allowing lever 182 to return to a position in which track 185 again engages rod 180. It will be seen that the embodiment of FIG. 23 further reduces the need for operator attentiveness and permits automatic limitation of the amount of liquid 44 to be employed in prewashing micropipet 210 and valve 100.

OPERATION OF THE INTEGRATED APPARATUS In pipetting operations carried out -with the apparatus 30 of the invention, the pipet-driving subassembly 80 is activated, as by making the appropriate connections to source of power and closing switch 41, to supply pressure and suction in tubes 65, 55 and pressure and suction lines 60, 50 in the pipettor 32. The pipettor 32 is grasped with the operator's hand 25 about handgrip 37, lifted from its receptacle 39 in housing 28, and moved to a desired position, limited only by the length of tubes 55, 65. A pipet 36 of the desired volume is selected, trigger 40 is depressed manually, and the pipettor engaging end 35 of the pipet 36 is inserted into socket 202. Trigger 40 is released, the pipet 36 being then operably engaged with the pipettor 32 by means of the retainer 300 and gasket 200. The pipet tip 236 is lowered into a liquid 44 to be pipetted, e.g. from beaker 45, and control button 38 is moved to the charging position (or in the embodiment of FIGS. 4 and 5, control button 138 is depressed) and the pipet 36 is charged. Since the pipet 36 will typically contain air prior to charging, the initial phases of charging provide air washing of micropipet 210, valve 100 and suction line 50.

After charging is complete the control means are operated to put valve 100 in the sealing mode and the charged pipet 36, liquid 44 and pipettor 32 are moved as may be desired to dispose pipet tip 236 within or above a beaker 46, or tube or the like into which the pipetted liquid is to be discharged. The appropriate control means, button 38 or pressure control button 139, are operated to put valve 100 in the discharging mode to discharge the liquid 44. As the pressurized discharge fluid (air or inert liquid) enters pipet 36, the valve 100 and micropipet are washed by the discharge fluid. After discharging is complete, the cycle can be repeated, utilizing the apparatus as a repetitive dispenser. Alternately, valve 100 can be operated to the sealing mode again, and the pipet 36 can be disengaged from the pipettor 32 and replaced by another pipet 36. In ordinary use it is desirable to provide a plurality of standardized pipets 36 having similar sealing faces 235, beveled ends 242 and collars 240, but adapted to pipet different predetermined volumes, for example, 0.1, l, 2, 5, l0, l milliliters and so on, the number of pipets 36 of each volume being selected according to the operators needs. In a typical analytical procedure, a single pipetting apparatus 30 may be used with several similar pipets 36 in succession to pipet several different 0.1 milliliter aliquots of several serum samples into a series of test tubes, and then employed directly with a single larger pipet 36 to pipet 5 milliliters of biuret reagent into each tube for analyses of protein by the biuret reaction. In most cases, the washing of micropipet 210 and valve 100 during the pipetting operation is sufficient to permit pipetting a series of different successive liquids with little or no detectable interference between liquid samples. Interference can be further reduced by employing a clean pipet for each liquid sample; also, the pipettor 32 can be rapidly cleaned or rinsed, when necessary or desirable, without disassembly of valve 100. During a typical series of pipetting operations, the trap is emptied from time to time as may be needed, for example, to prevent over-filling or accumulation of mutually incompatible materials in the trap 85.

Various modifications can be made in the pipetting apparatus 30. For example, the trigger grip 40, fork arms 310 and pocket 312 of the retaining means can all be included in a retaining member 300 of unitary construction as illustrated in FIG. 6. The walls of cylindrical and flared portions 248, 250 of socket 202 can be of glass or transparent plastic such as polystyrene or an acrylic resin or can include a transparent section, view port or the like to permit visual observation of the seating of a pipet 36 against gasket 200. In another modification each pipet 36 can be provided with its own gasket 200. In the pipet-driving subassembly 80, various means can be employed to sense the liquid level in the trap 85 and interrupt operation of the suction and pressure structure automatically when the liquid level in the trap 85 reaches a pre-determined height. Liquid level sensing means in trap can also be employed with an indicator light, buzzer or the like to signal the operator that the trap 85 should be emptied. Where mobility is not required, the pipettor 32 and driving subassembly 80 can be secured together by appropriate mounting means, and appropriate means can be employed to operate valve by electrical means employing solenoids, electric motors or the like or mechanical means such as described in my application Ser. No. 860,775, filed Sept. 24, 1969.

In summary, it will be seen that the apparatus of the invention provides a highly versatile and simple means for pipetting of fluids. While certain embodiments and variations of the invention have been described, a number of further variations and modifications can be made therein. For example, the pipet retaining means can be modified to include a second valve, socket and gasket to permit charging and discharging to be accomplished through appropriate lines via the additional valve in modifications similar to those described in my copending application, Ser. No. 860,775, filed Sept. 24, 1969. A plurality of pipets can be employed with a plurality of valves and additional lines to provide for simultaneous charging of all the pipets and discharge through successive ones of the pipets to a point of use. The use of a plurality of valves, lines and pipets can also be employed to provide for discharging of one pipet simultaneously with charging of another, as may be desired. Consequently, it will be seen that the invention is not limited to those embodiments specifically described above in detail.

What is claimed is:

l. Pipetting apparatus adapted for use with a plurality of interchangeable pipets, the apparatus com-prising a pipettor; means on the pipettor for selectively operatively engaging a pipet, said means including a micropipet in the pipettor adapted to communicate with a pipet operatively engaged therewith and gasket means for releaseably engaging an end portion of a pipet to provide sealingly communicative engagement of the pipet and micropipet; a hollow suction line in the pipettor; a hollow pressure line in the pipettor; valve means in the pipettor for providing selective communication and sealing between the suction and pressure lines and the micropipet, the valve means being operable between a charging mode in which the micropipet communicates with the suction line and is sealed from the pressure line, a sealing mode in which the micropipet is sealed from communication with both lines whereby a predetermined volume of fluid in the micropipet and a pipet engaged therewith is separated from communication with the suction line, and a discharging mode wherein the micropipet is sealed from the suction line and communicates with the pressure line; means for coupling the suction line to a source of suction adapted to draw a column of fluid through the micropipet and a pipet engaged therewith and into the suction line when the valve means is in the charging mode; means for coupling the pressure line to a source of fluid pressure adapted to provide pressure in the pressure line for discharging the micropipet when the valve is in the discharging mode.

2. Apparatus of claim 1 wherein the valve means is adapted to mechanically divide a fluid column which has been drawn into the micropipet and suction line during the charging mode into an integral fluid portion of predetermined volume enclosed by the micropipet and a pipet engaged therewith and a second integral fluid portion within the suction line, the valve means being adapted to divide the fluid column at a single 10- cation within the valve.

3. Apparatus of claim 1 further comprising manually operable means on the pipettor for disposing the valve means in a selected mode, and means for indicating the movement of a liquid column beyond the micropipet.

4. Apparatus of claim 3 wherein the indicating means comprise a transparent wall portion of the suction line to permit visual observation of a liquid column moving therethrough and a fluid resistance in the suction line adapted to impede the flow rate of such liquid column a predetermined distance along the suction line downstream of the valve.

5. Apparatus of claim 3 wherein the indicating means includes an electrical contact in the suction line and electrically conductive leads on the pipettor and on a pipet engaged therewith adapted to contact a liquid electrolyte to be pipetted, the indicator means being responsive to an electrical circuit through a column of the liquid electrolyte drawn into the suction line to the contact for sensing the completion of charging.

6. Apparatus of claim 5 further comprising biasing means in the pipettor for normally biasing the valve means toward the sealing mode, locking means for releaseably maintaining the valve means in the charging mode, and means responsive to an electric current conducted by a liquid electrolyte column through the valve means, micropipet and a pipet engaged therewith for releasing the locking means.

7. Apparatus of claim 1 wherein the valve means comprises a valve base mounted in the pipettor and having a bore therethrough, portions of the base surrounding the bore defining wall portions of the micropipet; and a valve block having separate bores therethrough, portions of the block surrounding the bores defining wall portions of the suction line and pressure line, said wall portions being selectively sealably engageable with the wall portions of the micropipet, means for mounting the valve block for movement relative to the valve base, and means for moving the valve block relative to the valve base between relative positions in which the micropipet communicates with one of said lines and is sealed from communication with the other of said lines, and a position in which the micropipet is sealed from communication with both lines by sealing engagement of wall portions of the micropipet with the valve block.

8. Apparatus of claim 7 wherein the valve base includes a hollow stud surrounding the micropipet and defining a wall portion thereof, the stud extending beyond a face of the valve base toward the valve block, the stud terminating in a sealing face adapted to sealingly engage a portion of a face of the valve block to provide sealing communication between the micropipet and a single one of said lines, and means including said stud for maintaining a major proportion of the opposed faces of the base and block spaced from each other to permit one of said lines to communicate with atmosphere between the opposed spaced faces when said line is sealed from communication with the micropipet.

9. Apparatus of claim 8 wherein the portions of the micropipet, suction line and pressure line at the 0pposed faces of the block and base are substantially cylindrical and having substantially similar diameters and substantially parallel axes; and wherein the valve block is mounted for relative movement in a plane substantially normal to the axes of the micropipet and lines.

10. Apparatus of claim 8 wherein the portions of the micropipet, suction line and pressure line at the opposed faces of the block and base are substantially cylindrical and having substantially similar diameters, wherein the sealing face of the stud extends radially outwardly from the micropipet a distance of between one and two times the diameter of the micropipet, and wherein the suction and pressure lines are spaced sufficiently from each other to prevent simultaneous sealing of both lines when the sealing face of the stud is sealingly engaged with a portion of the block face intermediate the suction and pressure lines.

1 l Pipetting apparatus comprising: pipet operating means including a pipettor; suction means for providing pipet-charging suction to the pipettor; pressure means for providing pipet-discharging pressure to the pipettor; hollow suction and pressure lines in the pipettor adapted to apply suction and pressure to a pipet; means including suction and pressure connecting tubes for providing communication between the suction and pressure lines and the corresponding suction and pressure means while permitting movement of the pipettor relative to the suction and pressure means;

sealing means on the pipettor for operatively engaging an end of a pipet; and

valving means on the pipettor for selectively charging a fluid into a pipet engaged by the sealing means and partially through such pipet into the suction line, selectively dividing fluid so charged into a continuous pipetted portion in the pipet and a single continuous fluid portion in the suction line, and selectively discharging the pipetted fluid portion under pressure from the pressure line, said valving means including a valve base having a cylindrical micropipet bore therein adapted to communicate with a pipet engaged by the sealing means; a valve block having cyclindrical suction and pressure line bores therein, the axes of said bores being parallel to the axis of the micropipet bore, means including wall portions of said parallel bores at a planar interface of the valve base and valve block for sealing a selected line bore in communication with said micropipet bore; means for movably mounting the valve block for limited motion relative to the base in a plane transverse to the parallel axes of the bores between a position in which a selected one of said line bores sealingly communicates with the micropipet bore and a position in which the micropipet bore is sealed; and means on the pipettor operably engaged-with the valve means for selectively moving the block relative to the base.

12. Apparatus of claim 11 wherein the suction connecting tube includes a portion which is wettable by the fluid.

13. Apparatus of claim llfurther comprising a fluid resistance in the suction line upstream of the valving means, said fluid resistance being adapted to impede the flow of liquid along the suction line.

14. Apparatus of claim 11 wherein the suction means and pressure means include the intake and exhaust of a single pump, said pump being adapted to operate independently of the operation of the valving means, and wherein the valving means includes means for selectively venting the suction line and pressure line when said lines are sealed from communication with a pipet.

15. Apparatus of claim 11 further comprising means operable independently of the suction means, pressure means and valve means for selectively regulating the pressure in the pressure line and means for independently regulating the suction in the suction line.

16. The apparatus of claim 11 wherein the valving means includes wall portions of the micropipet bore extending beyond the base toward the block and terminating in a planar face slidably sealingly engaged against a planar face of the block which includes wall portions of the parallel suction and pressure lines. Y

17. The apparatus of claim 16 wherein the valving means further includes means for limiting the relative planar motion of the base and block to a distance between about one and about six times the diameter of the micropipet bore.

18. In a pipetting apparatus comprising means for engaging a pipet to be employed in pipetting a liquid, means including a valve for selectively charging liquid into a pipet by suction, sealing liquid so charged in the pipet and discharging liquid from the pipet under pressure, the pipet having a sealing and face adapted to releaseably sealingly engage the pipettor and an opposed pipet tip through which pipetted liquid is to be charged and discharged, the improvement wherein the pipet includes an outwardly-extending collar a predetermined distance from the sealing end face thereof, wherein the apparatus further comprises a pipet-retaining member including a pair of fork arms adapted to receive a portion of the pipet intermediate the collar and tip between the fork arms, the fork arms being adapted to engage the pipet collar, the fork arms being mounted on the apparatus for movement of the fork arms relative to the pipet engaging means between a first position in which the fork arms and pipet-engaging means are in pipet-retaining relation to each other and a second pipet-releasing position in which the fork arms are displaced from the pipet-engaging means.

19. Apparatus of claim 18 wherein the apparatus includes a pipet-receiving socket adapted to slidably engage a portion of a pipet and guide the sealing face of the pipet toward engagement with the pipet-engaging means during motion of the fork arms toward the first position thereof.

20. Apparatus of claim 18 wherein the apparatus includes a pipet-receiving socket adapted to slidably engage a pipet and guide the sealing face thereof toward engagement with the pipet-engaging means, the socket having a peripheral lip adapted to slidably engage a corresponding end portion of a pipet to guide the sealing face into the socket.

21. Apparatus of claim 20 wherein the pipet engaging means includes a micropipet adapted to communicate with the interior of the pipet and a gasket surrounding the micropipet adapted to engage the sealing face of the pipet, and wherein the socket includes an inner portion adapted to guide the sealing face into sealing engagement with the gasket so that the micropipet communicates with the interior of the pipet, and an outer flared socket portion adapted to slidably engage an end portion of the pipet and guide the sealing face thereof into guiding engagement with the inner socket portion.

22. A pipet comprising a tubular body having, at opposed ends of the body, a pipet tip and a sealing face adapted to be releaseably sealingly engaged with a pipettor; the pipet being adapted to contain a predetermined volume of fluid between the tip and sealing face; and a collar extending outwardly from the pipet body, the collar being disposed on the pipet bodyintermediate the ends thereof and a predetermined distance from the sealing face thereof, the collar being adapted to be nestingly engaged by a corresponding portion of a pipet-retaining member on a pipettor.

23. A pipet of claim 22 further comprising electrically conductive means on the exterior of the pipet for conducting an electric current between the pipet tip and an electrical contact on a pipettor.

24. A pipet of claim 22 wherein the pipet body includes a beveled end portion at thesealing face, the beveled end portion extending about the sealing face and being adapted to slidably engage a wall of a pipetreceiving socket in a pipettor.

25. A pipet of claim 24 further comprising indicia disposed on the pipet body, said indicia being in standard volumetric units and indicating a volume corresponding to the predetermined internal volume of the pipet between the tip and sealing face thereof. 

1. Pipetting apparatus adapted for use with a plurality of interchangeable pipets, the apparatus com-prising a pipettor; means on the pipettor for selectively operatively engaging a pipet, said means including a micropipet in the pipettor adapted to communicate with a pipet operatively engaged therewith and gasket means for releaseably engaging an end portion of a pipet to provide sealingly communicative engagement of the pipet and micropipet; a hollow suction line in the pipettor; a hollow pressure line in the pipettor; valve means in the pipettor for providing selective communication and sealing between the suction and pressure lines and the micropipet, the valve means being operable between a charging mode in which the micropipet communicates with the suction line and is sealed from the pressure line, a sealing mode in which the micropipet is sealed from communication with both lines whereby a predetermined volume of fluid in the micropipet and a pipet engaged therewith is separated from communication with the suction line, and a discharging mode wherein the micropipet is sealed from the suction line and communicates with the pressure line; means for coupling the suction line to a source of suction adapted to draw a column of fluid through the micropipet and a pipet engaged therewith and into the suction line when the valve means is in the charging mode; means for coupling the pressure line to a source of fluid pressure adapted to provide pressure in the pressure line for discharging the micropipet when the valve is in the discharging mode.
 1. Pipetting apparatus adapted for use with a plurality of interchangeable pipets, the apparatus com-prising a pipettor; means on the pipettor for selectively operatively engaging a pipet, said means including a micropipet in the pipettor adapted to communicate with a pipet operatively engaged therewith and gasket means for releaseably engaging an end portion of a pipet to provide sealingly communicative engagement of the pipet and micropipet; a hollow suction line in the pipettor; a hollow pressure line in the pipettor; valve means in the pipettor for providing selective communication and sealing between the suction and pressure lines and the micropipet, the valve means being operable between a charging mode in which the micropipet communicates with the suction line and is sealed from the pressure line, a sealing mode in which the micropipet is sealed from communication with both lines whereby a predetermined volume of fluid in the micropipet and a pipet engaged therewith is separated from communication with the suction line, and a discharging mode wherein the micropipet is sealed from the suction line and communicates with the pressure line; means for coupling the suction line to a source of suction adapted to draw a column of fluid through the micropipet and a pipet engaged therewith and into the suction line when the valve means is in the charging mode; means for coupling the pressure line to a source of fluid pressure adapted to provide pressure in the pressure line for discharging the micropipet when the valve is in the discharging mode.
 2. Apparatus of claim 1 wherein the valve means is adapted to mechanically divide a fluid column which has been drawn into the micropipet and suction line during the charging mode into an integral fluid portion of predetermined volume enclosed by the micropipet and a pipet engaged therewith and a second integral fluid portion within the suction line, the valve means being adapted to divide the fluid column at a single location within the valve.
 3. Apparatus of claim 1 further comprising manually operable means on the pipettor for disposing the valve means in a selected mode, and means for indicating the movement of a liquid column beyond the micropipet.
 4. Apparatus of claim 3 wherein the indicating means comprise a transparent wall portion of the suction line to permit visual observation of a liquid column moving therethrough and a fluid resistance in the suction line adapted to impede the flow rate of such liquid column a predetermined distance along the suction line downstream of the valve.
 5. Apparatus of claim 3 wherein the indicating means includes an electrical contact in the suction line and electrically conductive leads on the pipettor and on a pipet engaged therewith adapted to contact a liquid electrolyte to be pipetted, the indicator means being responsive to an electrical circuit through a column of the liquid electRolyte drawn into the suction line to the contact for sensing the completion of charging.
 6. Apparatus of claim 5 further comprising biasing means in the pipettor for normally biasing the valve means toward the sealing mode, locking means for releaseably maintaining the valve means in the charging mode, and means responsive to an electric current conducted by a liquid electrolyte column through the valve means, micropipet and a pipet engaged therewith for releasing the locking means.
 7. Apparatus of claim 1 wherein the valve means comprises a valve base mounted in the pipettor and having a bore therethrough, portions of the base surrounding the bore defining wall portions of the micropipet; and a valve block having separate bores therethrough, portions of the block surrounding the bores defining wall portions of the suction line and pressure line, said wall portions being selectively sealably engageable with the wall portions of the micropipet, means for mounting the valve block for movement relative to the valve base, and means for moving the valve block relative to the valve base between relative positions in which the micropipet communicates with one of said lines and is sealed from communication with the other of said lines, and a position in which the micropipet is sealed from communication with both lines by sealing engagement of wall portions of the micropipet with the valve block.
 8. Apparatus of claim 7 wherein the valve base includes a hollow stud surrounding the micropipet and defining a wall portion thereof, the stud extending beyond a face of the valve base toward the valve block, the stud terminating in a sealing face adapted to sealingly engage a portion of a face of the valve block to provide sealing communication between the micropipet and a single one of said lines, and means including said stud for maintaining a major proportion of the opposed faces of the base and block spaced from each other to permit one of said lines to communicate with atmosphere between the opposed spaced faces when said line is sealed from communication with the micropipet.
 9. Apparatus of claim 8 wherein the portions of the micropipet, suction line and pressure line at the opposed faces of the block and base are substantially cylindrical and having substantially similar diameters and substantially parallel axes; and wherein the valve block is mounted for relative movement in a plane substantially normal to the axes of the micropipet and lines.
 10. Apparatus of claim 8 wherein the portions of the micropipet, suction line and pressure line at the opposed faces of the block and base are substantially cylindrical and having substantially similar diameters, wherein the sealing face of the stud extends radially outwardly from the micropipet a distance of between one and two times the diameter of the micropipet, and wherein the suction and pressure lines are spaced sufficiently from each other to prevent simultaneous sealing of both lines when the sealing face of the stud is sealingly engaged with a portion of the block face intermediate the suction and pressure lines.
 11. Pipetting apparatus comprising: pipet operating means including a pipettor; suction means for providing pipet-charging suction to the pipettor; pressure means for providing pipet-discharging pressure to the pipettor; hollow suction and pressure lines in the pipettor adapted to apply suction and pressure to a pipet; means including suction and pressure connecting tubes for providing communication between the suction and pressure lines and the corresponding suction and pressure means while permitting movement of the pipettor relative to the suction and pressure means; sealing means on the pipettor for operatively engaging an end of a pipet; and valving means on the pipettor for selectively charging a fluid into a pipet engaged by the sealing means and partially through such pipet into the suction line, selectively dividing fluid so charged into a continuous pipetted portion in the pipet and a single continuous fluid portion in the suction line, and selectively discharging the pipetted fluid portion under pressure from the pressure line, said valving means including a valve base having a cylindrical micropipet bore therein adapted to communicate with a pipet engaged by the sealing means; a valve block having cyclindrical suction and pressure line bores therein, the axes of said bores being parallel to the axis of the micropipet bore, means including wall portions of said parallel bores at a planar interface of the valve base and valve block for sealing a selected line bore in communication with said micropipet bore; means for movably mounting the valve block for limited motion relative to the base in a plane transverse to the parallel axes of the bores between a position in which a selected one of said line bores sealingly communicates with the micropipet bore and a position in which the micropipet bore is sealed; and means on the pipettor operably engaged with the valve means for selectively moving the block relative to the base.
 12. Apparatus of claim 11 wherein the suction connecting tube includes a portion which is wettable by the fluid.
 13. Apparatus of claim 11 further comprising a fluid resistance in the suction line upstream of the valving means, said fluid resistance being adapted to impede the flow of liquid along the suction line.
 14. Apparatus of claim 11 wherein the suction means and pressure means include the intake and exhaust of a single pump, said pump being adapted to operate independently of the operation of the valving means, and wherein the valving means includes means for selectively venting the suction line and pressure line when said lines are sealed from communication with a pipet.
 15. Apparatus of claim 11 further comprising means operable independently of the suction means, pressure means and valve means for selectively regulating the pressure in the pressure line and means for independently regulating the suction in the suction line.
 16. The apparatus of claim 11 wherein the valving means includes wall portions of the micropipet bore extending beyond the base toward the block and terminating in a planar face slidably sealingly engaged against a planar face of the block which includes wall portions of the parallel suction and pressure lines.
 17. The apparatus of claim 16 wherein the valving means further includes means for limiting the relative planar motion of the base and block to a distance between about one and about six times the diameter of the micropipet bore.
 18. In a pipetting apparatus comprising means for engaging a pipet to be employed in pipetting a liquid, means including a valve for selectively charging liquid into a pipet by suction, sealing liquid so charged in the pipet and discharging liquid from the pipet under pressure, the pipet having a sealing and face adapted to releaseably sealingly engage the pipettor and an opposed pipet tip through which pipetted liquid is to be charged and discharged, the improvement wherein the pipet includes an outwardly-extending collar a predetermined distance from the sealing end face thereof, wherein the apparatus further comprises a pipet-retaining member including a pair of fork arms adapted to receive a portion of the pipet intermediate the collar and tip between the fork arms, the fork arms being adapted to engage the pipet collar, the fork arms being mounted on the apparatus for movement of the fork arms relative to the pipet engaging means between a first position in which the fork arms and pipet-engaging means are in pipet-retaining relation to each other and a second pipet-releasing position in which the fork arms are displaced from the pipet-engaging means.
 19. Apparatus of claim 18 wherein the apparatus includes a pipet-receiving socket adapted to slidably engage a portion of a pipet and guide the sealing face of the pipet toward engagement with the pipet-engaging means during motion of the fork arms toward the first position thereof.
 20. Apparatus of claim 18 wherein the apparatus includes a pipet-receiving socket adapted to slidably engage a pipet and guide the sealing face thereof toward engagement with the pipet-engaging means, the socket having a peripheral lip adapted to slidably engage a corresponding end portion of a pipet to guide the sealing face into the socket.
 21. Apparatus of claim 20 wherein the pipet engaging means includes a micropipet adapted to communicate with the interior of the pipet and a gasket surrounding the micropipet adapted to engage the sealing face of the pipet, and wherein the socket includes an inner portion adapted to guide the sealing face into sealing engagement with the gasket so that the micropipet communicates with the interior of the pipet, and an outer flared socket portion adapted to slidably engage an end portion of the pipet and guide the sealing face thereof into guiding engagement with the inner socket portion.
 22. A pipet comprising a tubular body having, at opposed ends of the body, a pipet tip and a sealing face adapted to be releaseably sealingly engaged with a pipettor; the pipet being adapted to contain a predetermined volume of fluid between the tip and sealing face; and a collar extending outwardly from the pipet body, the collar being disposed on the pipet body intermediate the ends thereof and a predetermined distance from the sealing face thereof, the collar being adapted to be nestingly engaged by a corresponding portion of a pipet-retaining member on a pipettor.
 23. A pipet of claim 22 further comprising electrically conductive means on the exterior of the pipet for conducting an electric current between the pipet tip and an electrical contact on a pipettor.
 24. A pipet of claim 22 wherein the pipet body includes a beveled end portion at the sealing face, the beveled end portion extending about the sealing face and being adapted to slidably engage a wall of a pipet-receiving socket in a pipettor.
 25. A pipet of claim 24 further comprising indicia disposed on the pipet body, said indicia being in standard volumetric units and indicating a volume corresponding to the predetermined internal volume of the pipet between the tip and sealing face thereof.
 26. A pipet of claim 25 wherein the indicia on the pipet indicate a volume greater than the total internal volume of the pipet by a predetermined volumetric increment corresponding to the volume of a micropipet of a pipettor which is adapted to operatively engage the pipet, said volumetric increment being a minor proportion of the total internal volume of the pipet.
 27. A method useful for pipetting, the method comprising: a. coupling a pipet to a tubular suction line having a moveable wall and a tubular pressure line having a moveable wall to form a selective three-way intersection of the pipet with the lines; b. applying fluid suction in the suction line; c. continuously applying fluid pressure in the pressure line; d. charging the pipet, including moving selected wall portions of the pressure line to seal said line from the intersection, moving selected wall portions of the suction line to provide communication between the suction line and the pipet, and drawing a liquid to be measured into the pipet and partially therethrough into the suction line; e. thereafter moving selected wall portions of the suction line to seal between the suction line and the intersection, thereby dividing the portion of liquid drawn into the suction line from the portion remaining in the pipet, said wall portions being moved to provide the seal at a single location in the line; and f. thereafter moving the selected wall portions of the pressure line to provide communication between the pressure line and the intersection.
 28. The method of claim 27 wherein the moveable walls of the suction and pressure lines include relatively moveable opposed wall portions, and wherein the respective opposed wall portions are moved in a plane perpendicular to the axis of their respecTive line. 